RWBY: Tar
by Falcyon
Summary: In an event that by all accounts never existed, a synthetic Grimm escapes into the wild, and forces its way into Yang's life. With its help, she feels ready to take on the hostile world. But there are some side-effects she must deal with... Rated M for language and graphic descriptions of sex.


**Author's Note:** (Alright, second time trying this)

Hey there! It sure has been a while since I've uploaded anything here. Hopefully this fic makes up for that! I will be uploading a new chapter once every other Wednesday, starting with today (even though it's technically Thursday now).

Super special thanks to The Draigg for editing and being a fantastic friend! Go check out his work too!

This story is rated M for a reason. Please do not read if you are under 18 or not willing to read sex scenes.

I do not own RWBY, of course. Roosterteeth does. You should know that by now, silly.

Please enjoy!

 **Prologue**

On a nondescript island off the coast of Vale was a classified facility. Built into the side of a small outcropping of rock, and half submerged in the sea, it was so well hidden nobody had any reason to deny its existence or purpose. The lowest level held the main laboratory. For safety and testing purposes, it was sealed in a foot of lead and had three airtight security doors leading to it. The three inhabitants were currently opening the final titanium door leading inside. Each one had a yellow hazmat suit on.

"...like I was saying," one of them said, "it'd only make sense if the proteins were assembled in that specific order. And besides, we haven't been able to test Grimm cells because of how quickly they disintegrate after communication is severed from the nervous system."

"That's why we called you here, Professor Azure," the shortest one responded. Then he stopped, holding the professor back. "Just remember, you're on contract not to say anything to anyone until you've been notified by the proper people."

"Of course, Mintz," Azure assured the younger man. "Now what is it you brought me here for?

"Vermillion, if you'd be so kind?" Mintz said, nodding to his female associate.

"You bet," the female rabbit faunus said with a smile. She strode over to a console and hit a button.

In the center of the room, a large cylinder opened up, revealing a glass tube with a dark liquid inside.

"What is that?" Azure asked, walking closer.

"Professor," Mintz said with a smile, "You're looking at the first ever synthesized Grimm."

"Where?" Azure came up to the glass and peered inside, looking for movement in the liquid. He waited a bit, then knocked on the glass. What he got was not at all what he expected.

With a quick lurch, a tendril of black muck snaked up the side of the tube. Azure jumped back with a small yell. His companions chuckled.

"That's it, professor," Vermillion said. "G-046-u, nicknamed Shoggoth. It's a Grimm with no skeleton or nervous system. We haven't figured out exactly how it managed to work yet, but we're hypothesizing it has something to do with our last batch of Nevermore eggs and a brilliant stroke of luck with a collection of Dust samples."

Mintz nodded. "There have been some theories that Grimm came from an ancient bacteria in the moon, but since Dust doesn't work above our atmosphere, nobody's thought to combine Dust and powdered moon rock."

Azure collected himself and looked at his colleagues, then back to the black liquid, then back to them.

"You're serious?"

"A hundred percent, sir."

"And it's stable?"

"More molecularly stable than a healthy Beowulf, actually."

"Have you tested it for normal Grimm behavior and habits?"

"Yes…" Vermillion hesitated, sharing a look with Mintz.

"What?" Azure said. "What was that look for?"

"Well…" Mintz said, "It seems to have a different appetite than most Grimm."

"Which is...?" Azure questioned, becoming increasingly irate. "Look, do you want my help studying this creature or not?"

"We…um…stimulated it with our blood."

"You what?!" Azure raised his voice.

"Grimm only hunt and eat humans and faunus, so it made sense." Mintz said, backing Vermillion up.

"I-this breaks protocol on so many levels."

"This facility is built upon the standard of breaking protocol. What we're doing is technically illegal, but we've been sanctioned by someone powerful enough to let the few in the government that know about this to look the other way."

"Alright," Azure said with a sigh. "So what was the result of your test?"

"It…well, to put it bluntly, the sample adopted my heat."

"…what?"

"I'm…um…I went into heat yesterday…"

"…you're kidding. How did you find out?"

Mintz flushed bright red. "Um…Vermillion and I…uh…" He and Vermillion avoided Azure's stern gaze.

"First of all, workplace romance is a terrible idea. Second, I meant how did you find out about the Grimm adopting your…condition?"

"We…uh…"

"We had sex in here," Mintz said. "The sample with Vermillion's blood became agitated and tried to come out of its container."

"You-I-why the hell-" Azure sputtered.

He stared at them. The two lovers wore fearful expressions. Azure sighed. This was too stupid for him. Whoever the hell had hired these two needed to be fired and slapped in the face.

"That doesn't prove it's adopted your sex drive-"

"Professor!" Vermillion screamed, pointing behind him.

Azure turned just in time to see the large Grimm tremble. It looked like it was boiling. Or breathing. Or both. A small hairline fracture appeared in the glass.

"It…it's reacting to the negativity!" Mintz yelled, running to the door and opening it. "We have to get out of here!"

Azure opened his mouth to reprimand the younger man, but was silenced by a crinkling sound around his feet. He looked down. The Grimm had leaked out of its container and was pooling on the floor around his plastic hazmat boots.

"Oh-" was all he was able to exclaim before tendrils reached up and restricted his limbs and neck. His eyes bulged as he was strangled by the creature. It found a weak point in the suit and sloshed its way inside.

Vermillion started to scream. Mintz grabbed her and pulled her through the door before closing it.

"We need to go back for the professor!" Vermillion wailed.

"We can't! He's dead!" Mintz huffed.

They ran down the corridor, closing all the airtight doors behind them. In the lab, the Shoggoth slowly absorbed Azure's corpse, feeding on the nutrients the body held. It grew, becoming about the size and volume of a basketball.

"Verm," said Mintz with a heavy breath, "seal the vents. We can't let it escape."

Vermillion sank to the ground in tears. "This is all my fault…" Her words came as a trembling whisper. She ripped the helmet off her suit and breathed the cold air, letting her bunny ears out. They drooped down. Big tears rolled down her face and splashed to the floor. "W-we shouldn't have used my blood…"

"We shouldn't have done a lot of things, Verm." Mintz said with a mix of fear, gentleness, and anxiety all coming together in his voice. "But look where we are. We're in danger. And the only way we can get out of this is to seal the lab, get off base, and initiate the self-destruct sequence."

"I…you're right…"

"Come on, let's get out of here together." Mintz said. "Let's get as far away from here as possible and live the rest of our lives knowing we were able to beat this."

Vermillion's watery eyes moved to Mintz's reassuring smile. She gave a small nod. Then she heard a noise that made her blood freeze.

Drip…

Drip…

Black goo dripped out of Mintz's mouth. His smile stretched wider as more and more poured out, coating Vermillion's left leg.

"M-Mintz…?" Vermillion could barely form any semblance of response to what she was seeing.

"Mintz?" Mintz asked, his voice fluctuating as if he was trying to change his mood. "Mintz…no, not Mintz…"

He paused. Vermillion shivered in fear, looking around for a way to free herself. She whimpered when she saw the blackness oozing around the floor, pouring from a vent. It had snuck up on them.

She kicked out, landing a solid hit on Mintz's chest. He went flying backward, slamming into a pillar on the opposite side of the room. Vermillion picked herself up, and in a mad dash, sprinted through the puddle of Grimm to a large array of controls for the base. She grabbed inside her suit for her key, and fished Mintz's out of his pocket. The Grimm was oozing out of his mouth at an alarming pace now. His body twitched and spasmed.

Vermilion shoved the two keys into their respective holes and turned them. A panel in the middle of the console opened up to reveal a large red button that said DETONATE. She slammed it down.

"DIE, YOU ABOMINA-"

The facility tore itself apart in the explosion. Large chunks of rock flung themselves into the sea as water crashed into the new hole in the cliff face. The sea claimed what was left of the twisted structure.

Deep beneath the waves, a small cloud of blackness drifted aimlessly. What little remained of the Shoggoth was still sentient. It couldn't move in the water, so it let the current carry it. Whatever consciousness it had told it to seek out humans. Powerful humans. So it bode its time. It waited patiently, knowing one day it would arrive somewhere it could feed.

 **Chapter 1 : An Unexpected Penetration**

Yang Xiao-Long lay in her bed and stared at the ceiling. She'd refused to leave the house, ever since what had happened at Beacon Academy a couple of months ago. All that had happened, all that she'd lost… She didn't want to admit she had given up, but her morale had been dashed and was sinking lower and lower every day. Her teammates had all left. Her bold younger sister Ruby had run off to go continue the search for whoever had caused the destruction of Vale. Weiss had been scooped up by her overprotective father, no doubt. Blake… well, she was gone. Gone for good, most likely. Yang didn't blame her. She just wanted answers. Blake knew that man who had… who had been named Adam. He was obviously a high ranking member of the White Fang. Blake was hurt, and Yang had been forced into a trap as a result. Blake had run away while Yang was still unconscious, probably to save the pain of responsibility, just like their first year… What a coward…

Yang lifted what was left of her right arm. A stump that ended halfway down her bicep rose slowly, almost as if to taunt her. Her weapons, her fighting, all the years of training… It was all for this. This loss. This pain. It sometimes ached like it was still there. On occasion she would wake up, hoping beyond hope that her arm had somehow grown back. A quiet knock on her bedroom door partially snapped her out of the haze of her depression. She sat up, her sheets rustling quietly.

"Yang?" came a concerned voice. "I…well, I made breakfast. Waffles and sausage, like back before you went to Signal…" The voice trailed off. "Come to the kitchen if you're feeling hungry… or I can bring you some, if you want."

Yang grunted and fell back into her bed.

"Dad?" she asked quietly. Her voice crackled from disuse.

"Yeah?"

"I'm gonna take a shower… uh… don't run any water…"

"Ah, alright…"

Yang propped herself up and swung her feet out of bed. She paused, took a breath, and shifted to push her feet on to the cold floor. She stood up, groaning again. The frigid air nipped at her bare arms and legs. Her top and shorts barely did anything to shield her from the goosebumps that rose as a result.

"Yang, I'm going out to the store. I'll be back in a bit. Do you need anything?"

"No…I don't think so." Yang responded. She stretched her arm and yawned.

"Alright then. I'll see you in an hour or so, then?"

"Yeah. Bye, dad."

"Bye, Yang. I love you…"

There was an awkward silence as Tai-Yang waited for her response. When she didn't answer, he shuffled off. Yang heard the front door open and close. She knew her father meant well. He had always been supportive and understanding. She also knew that her actions in the past weeks since the incident were less than gracious toward her family. Especially, and unjustly, toward Ruby. She was essentially the last member of their team that hadn't left. That was until she teamed up with the remainders of Team JNPR and left without Yang. Of course, she admitted she couldn't be of much use, considering her condition.

She shuffled to the door. The handle felt cold in her hand. The entire house was chilly from the previous night's snowfall. The hall was even colder than her room. She padded her way to the bathroom. Her reflection in the mirror greeted her with its gaunt face and unruly, oily hair. She had trapped herself in her room for far too long.

Man… I look terrible.

Yang swept her hair back behind her. She turned on the water as hot as it would go and waited for the water heater to warm up. It always took long this time of year. The shower was deafening against the silence of the house. Yang stripped out of her pajamas. Despite her brooding indoors for several months, her body had remained relatively toned. That was thanks in part to her Semblance allowing her to burn fat with minimal exercise.

The showerhead sputtered for a second, waking Yang up a bit. The warm mist in the air alerted her to the fact that the shower was now warm. Yang pulled the shower curtain back and stepped in. The hot water gave her a jolt at first, but as her body relaxed and adjusted to the temperature, it became a soothing pulse against her cold skin. Bottles of shampoo, conditioner, body wash, and all sorts of beauty products lined the lips of the tub. Yang use to use them all to keep her hair nice, but what was the point anymore? She wouldn't go outside, she couldn't fend for herself anymore, and most of all, she didn't want to. She was fine living the rest of her life in this house.

The showerhead sputtered again, spitting water erratically across Yang's bare back. Yang picked up a shampoo bottle and flipped the cap with her fingers. She outstretched her other arm –

Frustration seethed through Yang. The stump was mocking her again.

You could have done more. You could have saved Blake. You pitiful, self-loathing coward!

Yang's eyes flashed red as she threw the bottle against the floor of the tub. It clattered loudly before rolling to a stop at the drain. She took in a few heavy breaths. The humid air made those breaths harder to make. She calmed herself down enough to where she could think clearly. She bent down and picked up the shampoo bottle. The water above her sputtered for a much longer interval, and stopping altogether for a second, before resuming its normal flow.

Unbeknownst to her, there was something that had just slithered its way through the pipe and shot out through the showerhead with the water. A dark rubicund mass about the diameter of a cantaloupe was splattered against the back of the tub. The Shoggoth could sense a strong Aura in this chamber. It pulsed, getting a sense of its surroundings. It sensed something it recognized from its birth. The musk of a female. A mate. It dripped down the dub, allowing the water to carry it directly to its new mate's feet.

Yang stood up. The bottle was fractured and leaking shampoo. So much for that. Yang sighed dejectedly. Then she felt a jolt at her feet. Cold water. Did she spend too much time drifting off instead of taking care of her business? She felt stupid. Then she froze. The cold feeling was traveling up her feet and was now around her ankles. She looked down.

A black mass was swirling and gyrating around her feet, and it had engulfed her feet completely. She let out a yell and tried to step away. The mass held her to the surface of the tub, however, and it began to tendril its way up her legs faster. Yang tried desperately to come up with a way to get rid of it. Water wouldn't flush it away. Maybe the opposite would work.

Yang fired up her Aura. The air grew unbearably hot for any normal person. Yang's skin was ablaze with heat and unbridled energy. She would burn this slime off her. Her hair had the look of a bonfire as it swayed from the radiating power. The slimy…thing slowed down. Yang celebrated in her head as she turned the heat up even more. Now the water from the shower couldn't even touch her skin. It was evaporating into thick steam about six inches away.

The Shoggoth could feel the heat its currently unwilling mate was producing. This would be the perfect mate for cultivation and reproduction. However, it needed a way to stop her from destroying it. So it lurched at the only safe haven it could find.

Yang let out a gasp as she saw and felt the sticky black substance jump and latch onto her pubic mound. It started to worm its way into her entrance. She could feel it writhe around as it slowly made its way up through her vagina.

"No!" Yang cried. She tried to heat her body up even more. At this point, the plastic shower curtain was melting, and the tiles around her fractured with loud cracks. But the slime held fast. Yang could feel her aura dropping quickly. She was out of practice. She cursed herself just as her barriers dropped and she fell to the floor of the bathtub. She desperately swatted at the jiggling mass between her legs. All she did, though, was succeed in getting it stuck to her hand as well. It pulsed faster, stirring around inside her. Yang let out a whimpering moan.

The Shoggoth absorbed her juices as it creeped deeper into its mate's innermost chambers. It could also feel the hand it was stuck to. This mate was going to need to relax to allow for consensual breeding. It used an ability it had received from its last blood mate. Strong pheromones released into the air and penetrated the walls it was pushed up against.

Yang shuddered. Something felt…different. Her fear was dying out and being replaced with…pleasure. Why? This monster, whatever it was, was violating her, and yet she felt fine. In fact, she felt better than fine. Deep down, she knew something was wrong, but she could barely control her own thoughts anymore. They were being drowned out with a basic, primal instinct.

Mate.

Yang moaned. The Shoggoth was now sliding in and out of her pussy with a newfound energy. It also began sucking and pulling on her clit. Yang's core melted with a different kind of heat than what she had tried to use to get rid of it. Now it was to draw it deeper within. Yang wanted it to pump through her and satisfy her newfound sexual urges. She wobbled to her knees and bent over, turning her shapely ass to the ceiling.

The Shoggoth felt a shift and could sense another opening. More…

It plunged into Yang's tight asshole and penetrated deep and fast. Yang couldn't control her actions anymore. All she wanted was for the pleasure to build until she broke. She licked her hand, scooping the slime into her hungry, drooling mouth. It tasted strange, albeit somewhat familiar. It was a cross between the taste of her own juices and something else. Something quite unnatural. She didn't care though. She was unable to care about anything but the slime fucking her and violating deeper and deeper.

The first tendril of goo to enter her had made its way into her womb. It twisted and spiraled around inside her. Yang moaned and drooled more, letting it violate her hungry insides. Her mind was as misty and dense as the air around her. The sludgy tentacle fucking her asshole was now playing around in her intestines. Yang let her tongue loll out of her mouth. Her eyes rolled up into her head. Nothing could beat the overwhelming sensation this slime could give her. Nothing at all.

Her body was starting to react in strange ways. Her breasts started to produce milk, and her ovaries released one egg each. The Shoggoth latched onto her eggs and engulfed them. It would use these to grow. Yang felt her stomach swell as the Shoggoth expanded inside her.

"Ohhhhhh" she moaned, barely able to register anything but pleasure at this point.

The Shoggoth curled around every nook and cranny of Yang's uterus and vagina. Yang felt herself tense up, and the Shoggoth responded by pushing itself out of her entirely, lifting itself off her, and then plunging back inside. Yang screamed from the sudden escape and return to her cunt.

"I-I-I…" Yang mumbled. She was trying to yell that she was about to cum. She could sense that it was aware of this, though, because it pumped in and out of her with newfound fervor. The tentacle in her ass was now pushing into her stomach, meeting up with the slime she had swallowed. She was being completely filled up. She loved it. Her body jerked and spasmed, and the floodgates opened. Yang came harder than she'd ever done before. Her juices were absorbed by the slime, which continued to slosh in and out of her. It slowed down, before stopping and pouring out of the now unconscious broken girl. It swung a tendril and slammed the shower control to the off position. It could use this mate to get farther. To grow, and reproduce even more. It felt around her body before settling on a break in her symmetry.

It would settle here for now.


End file.
